Tag: Southern Ocean

2019 was Australia’s hottest and driest year on record

Adelaide 5000

The data is in and 2019 has topped the Bureau of Meteorology’s (BOM) charts for average and maximum temperatures as well as the lowest annual rainfall across the country.

Key points:

  • Australia’s annual mean and maximum temperatures both broke records set in 2013
  • The national area average rainfall was the lowest on record going all the way back to 1900
  • The hot and dry conditions are the result of a strong Indian Ocean Dipole and background warming

It will come as no surprise to those suffering through this horror fire and heatwave season that the conditions leading up to it were the worst on record.

The new figures arrived as large parts of the country brace for more dangerous fire conditions over the next few days.

BOM will comment when its official report comes out next week, but the numbers speak for themselves.

Australia’s annual mean temperature was 1.52 degrees Celsius above the 1961-90 average of 21.8C — well above the previous hottest year (2013) at 1.33C.

External Link:

The difference in annual mean temperatures from the 1961-90 average

Also, the daytime temperature record was smashed, with the average maximum temperature of 30.69C coming in 2.09C above the 1961-90 average.

The previous record, set in 2013, was 30.19C.

External Link:

The difference in annual maximum temperatures from the 1961-90 average

Overnight temperatures didn’t surpass the record, but they were still the sixth hottest on record and well above average at 0.95C over the 15.1C 1961-90 average.

Meanwhile the drought has dragged on.

The national average rainfall total for the year was 277.63 millimetres, well below the previous record of 314.46mm in 1902 during the federation drought.

External Link:

Australia's annual rainfall from 1900 to 2019

The 1961-90 period is an internationally used standard as a period of good weather records used for data comparisons.

These values are calculated based upon gridded data from across Australia.

The country is broken up into a 0.05-degree grid by longitude and latitude, which is roughly 5km by 5km, with each grid assigned a maximum temperature based on the weather stations around it.

The average of all of the grids for every day of the year is then output.

Using the same gridded dataset, Australia broke the record for its hottest day on record two days in a row last month, with the nation’s average maximum temperature smashing the previous record (40.3C) to reach 40.7C and then 41.9C a day later.

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Why so hot?

The record-breaking year was especially noteworthy because it occurred without an El Nino event, the climate driver most commonly associated with hot dry conditions in Australia.

While the Pacific Ocean remained neutral, the main climate driver was the incredibly strong positive Indian Ocean Dipole (IOD).

The IOD has been working to generate rising air and rain over eastern Africa but hot descending air over Australia.

It is associated with drought and hot conditions over eastern Australia as well as with a delayed monsoon, all of which have been the case this summer.

Late last year, an unusual sudden stratospheric warming (SSW) event also added to the hot dry conditions by shifting the westerly winds, which usually lurk over the Southern Ocean, up onto the continent.

Video: This is how sudden stratospheric warming occurs

(ABC News)

This event was also associated with a strong positive phase of the Southern Annular Mode (SAM), again encouraging hot dry conditions.

And this is all on top of the anthropogenic global warming trend; BOM records show Australia has warmed by just over a degree since 1910, with most of the warming occurring since 1950.

What now?

Thankfully the positive IOD and negative SAM have decayed and the BOM’s outlook for the next three months is decidedly more neutral for rainfall, although temperatures are likely to remain above average for most of the country.

It is finally beginning to look like more tropical weather is returning to our north, with the chance of a cyclone developing early next week and tropical rainfall expected to move into inland Western Australia over the next few days.

But for those in the south, while a return to neutral conditions is better than drier than average, average conditions over summer are still hot and dry.

Until there is widespread rainfall, fire and heatwave conditions will continue.

External Link:

The weather bureau's outlook for January to March

Source: https://www.abc.net.au/news

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